I’m not an attorney, but as far as I know you are not legally required to solicit any number of bids. However, you are required to follow any policies your organization may have in place. We did a remodel of our main branch a few years back and I had our architect send it out to bid. There were only two bidders, and we chose the best of the two.

Van Buren has no such purchasing policy, but my last library did have one. I’m attaching it here.